The NIH estimates that 28 million Americans have some degree of hearing impairlnent, many significantly enough to affect the quality of their lives. About 1/3 of the hearing-impaired individuals are over 65 years of age. For those who are profoundly deaf, cochlear implants offer the only means in which to restore some hearing ability. Halt of all implant recipients are over the age of 55. Although there is large variability in performance, 70-80% of implant recipients achieve acceptable speech recognition. The long-term goal of this project is to develop a way to increase the number of individuals who regain speech recognition abilities with multichannel implants and/or improve their recognition of frequency-specific information. If a significant number of the surviving ganglion cells in the damaged inner ear can be induced to regenerate their peripheral processes, more focal stimulation could be produced with lower currents. The proposed studies will determine if a chemokinetic substance: can be delivered in (or with) a cochlear electrode-array implant; will induce nerve fibers to regenerate; and will direct these fibers to the area of the implant. There has been growing interest in developing ways in which to stimulate the biological replacement of damaged parts of the inner ear. Hair-cell regeneration occurs in the noise-and drug-damaged avian inner ear under certain circumstances. But, biological replacement of damaged parts of the peripheral auditory system remains a distant future goal because replacement of hair cells alone is not sufficient to restore hearing ability. The new hair cells must be oriented correctly, must be bathed in the appropriate extracellular fluids, and must be appropriately innervated. We have previously found that some nerve fibers spontaneously regenerate in noise-damaged chinchilla ears and that these fibers are not part of the efferent cochlear system. We determined that Schwann cells are intimately involved in this regeneration response. We will attempt to ehhance the number of regenerated fibers in the noise-damaged ear by administering to the cochleas basic fibroblast growth factor, a mitogen for Schwann cells, or nerve growth factor, a promoter of neuritogenesis.